U.S. patent application number 12/306952 was filed with the patent office on 2010-03-11 for cmos circuits combining high voltage and rf technologies.
This patent application is currently assigned to X-FAB SEMICONDUCTOR FOUNDRIES AG. Invention is credited to John Nigel Ellis, Jun Fu, Paul Ronald Stribley.
Application Number | 20100059851 12/306952 |
Document ID | / |
Family ID | 36888333 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100059851 |
Kind Code |
A1 |
Ellis; John Nigel ; et
al. |
March 11, 2010 |
CMOS CIRCUITS COMBINING HIGH VOLTAGE AND RF TECHNOLOGIES
Abstract
A CMOS circuit comprises at least one high voltage transistor
(having gate and drain operating voltages of greater than 8V) and
at least one high frequency capable transistor (having a maximum
switching frequency of between 100 MHz and 1000 GHz) wherein said
transistors are integrated on the same semiconductor substrate so
as to allow the simple integration of high voltage circuits and RF
(radio frequency) CMOS circuits on the same integrated circuit.
Inventors: |
Ellis; John Nigel; (Devon,
GB) ; Stribley; Paul Ronald; (Devon, GB) ; Fu;
Jun; (Erfurt, DE) |
Correspondence
Address: |
THOMPSON HINE L.L.P.;Intellectual Property Group
P.O. BOX 8801
DAYTON
OH
45401-8801
US
|
Assignee: |
X-FAB SEMICONDUCTOR FOUNDRIES
AG
Erfurt
DE
|
Family ID: |
36888333 |
Appl. No.: |
12/306952 |
Filed: |
June 27, 2007 |
PCT Filed: |
June 27, 2007 |
PCT NO: |
PCT/GB07/50363 |
371 Date: |
October 21, 2009 |
Current U.S.
Class: |
257/500 ;
257/E27.046 |
Current CPC
Class: |
H01L 27/0629 20130101;
H01L 29/7835 20130101; H01L 21/823857 20130101; H01L 21/823878
20130101; H01L 21/823892 20130101; H01L 27/0922 20130101 |
Class at
Publication: |
257/500 ;
257/E27.046 |
International
Class: |
H01L 27/08 20060101
H01L027/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2006 |
GB |
0612950.6 |
Claims
1. A CMOS circuit comprising at least one high voltage transistor
having gate and drain operating voltages of greater than 8V and at
least one high frequency capable CMOS transistor having a maximum
switching frequency of between 100 MHz and 1000 GHz wherein said
transistors are integrated on the same semiconductor substrate so
as to allow the simple integration of high voltage circuits and RF
(radio frequency) CMOS circuits on the same integrated circuit.
2. A CMOS circuit as claimed in claim 1, wherein said high
frequency capable transistor has a maximum switching frequency of
between 100 MHz and 200 GHz.
3. A CMOS circuit as claimed in claim 1 which also includes at
least one low voltage transistor having gate and drain operating
voltages of less than 8V integrated on the same said semiconductor
substrate.
4. A CMOS circuit as claimed in claim 3, wherein said low voltage
transistor has a maximum switching frequency of between 100 MHz and
1000 GHz, and can operate at RF frequencies.
5. A CMOS circuit as claimed in claim 3, wherein said low voltage
transistor forms part of a circuit arranged for electrical signal
processing or for use as a memory, including digital logic, DSP,
analog functions, computer processors (CPU), ROM and SRAM.
6. A CMOS circuit as claimed in claim 1, which further comprises
one or more deep n-well diffusions and deep p-well diffusions to
create regions of high voltage capable transistors.
7. A CMOS circuit as claimed in claim 6, wherein regions of deep
n-well diffusions are isolated from each other by regions of deep
p-well diffusions.
8. A CMOS circuit as claimed in claim 1, wherein multiple deep
n-well diffusions are formed within the same said substrate which
have different doping levels to allow optimized high voltage
components to be made using them which can then co-exist on the
same integrated circuit.
9. A CMOS circuit as claimed in claim 1 wherein low voltage CMOS
transistors are fabricated within deep n-well diffusion regions in
said substrate, so as to allows them either to interface more
easily to high voltage circuits by applying an offset voltage to
the n-well, or alternatively to be completely isolated from high
voltage circuitry to prevent electrical interference from high
voltage circuitry.
10. A CMOS circuit as claimed in claim 1 which also includes on
said substrate other components which are useful to create RF
circuits, including any or all of the following components:
semiconductor diffusion resistors, doped polysilicon resistors,
metal resistors, interleaved metal capacitors, interleaved
polysilicon capacitors, semiconductor junction diodes, metal
semiconductor schottky diodes, diode junction varactors, MOS diode
varactors, variable capacitors and greater than 0.5 um thickness
metal inductors.
11. A CMOS circuit as claimed in claim 1, which comprises an RF
transmission component, and an RF circuit which operates at low
voltage less than 8V interfaced on the same substrate to a higher
voltage greater than 8V circuit which is arranged to have
sufficient voltage and power supplying capability to adequately
stimulate said RF transmission component.
12. A CMOS circuit as claimed in claim 11, wherein said RF
transmission component is a radio antenna, which can be used to
transmit radio waves which can communicate with other remote RF
detection circuits.
13. A CMOS circuit as claimed in claim 1, which comprises an RF
circuit which operates at low voltage less than 8V interfaced on
the same substrate to a higher voltage greater than 8V circuit so
that the low voltage RF circuit can efficiently detect and process
radio frequency information supplied from a distant source
transmitter and then pass on the controlling signals to the
latter.
14. A CMOS circuit as claimed in claim 13, wherein said higher
voltage circuit is arranged to provide significantly higher voltage
supplying capability to control other equipment such as motors or
electronic displays which would otherwise be beyond the voltage
supplying capability of said low voltage circuit, so that higher
voltage (greater than 8V) electrical equipment can be controlled
remotely by means of radio wave information transmission using a
single integrated circuit.
Description
[0001] The invention relates to CMOS circuits which combine high
voltage and RF technologies.
[0002] Modern CMOS technology is capable of providing transistors
which have the capability of operating at frequencies of 1 GHz or
more. This enables them to provide functionality in radio frequency
(RF) communications either for transmitting or receiving, or both.
RF communications are increasingly important in today's society as
people use more and more personal and portable equipment such as
mobile telephones, laptop computers with wireless networking
capability and music systems. In automotive applications, car
electronics is likely to exploit RF communication links in future
for navigation, communication, radar (anti-collision avoidance,
steering in difficult conditions like fog) and night vision (IR
cameras for fog and night-time identification of animals and people
who may be on the road).
[0003] RF CMOS circuits are those which can be used for the
detection, processing or transmission of radio waves or microwaves
which are electromagnetic waves which have a frequency range of
about 10 kHz to 1000 GHz. Hence these circuits need to be made from
high switching speed capable components which can operate usefully
at radio wave or microwave, RF frequencies. RF CMOS components are
made using structural configurations which enhance the switching
speed capability of the transistors eg by using multiple transistor
gates connected in parallel to minimise gate connection series
resistances and minimise diode junction parasitic capacitances
inherent in the device.
[0004] Another field of growing importance is the increasing use of
high voltage electronics. High voltage electronics refers to any
device which is powered from a power supply voltage rail above the
normal supply voltage for that technology. For example, as
geometries have shrunk from 1 micron and above, which operated at
5V, to 0.35 micron, the power supply became 3.3V. At smaller
geometries the power supply voltage is approximately the technology
geometry expressed in microns multiplied by 10. For example, 0.18
micron technology operates from 1.8V; and 0.13 microns from 1.2 to
1.3V. Where such geometries are given (eg. 0.18, 0.35, 1 micron)
they refer to the typical CMOS gate length. Automotive systems
operate on essentially the 12V standard which has been used for the
last 40 years or so. To be able to drive devices at 12V,
transistors capable of withstanding 40V for a few seconds is
necessary, in order to ensure functionality in the event of a power
surge. Transistors which can support these higher voltages need to
be designed specifically for these conditions.
[0005] Potential applications for RF communications with high
voltage applications can be foreseen where high voltage transistors
can be controlled through an RF communication link. These can be
exploited in mains-operated equipment: for example, switch-mode
power supplies; and monitoring equipment, such as industrial
controllers; wireless networks such as computer communication
systems using infra-red links; and so on where not only are the
high voltage transistors required but also high speed transistors
to provide communication. In this way it would be possible to
establish remote links to security equipment, using RF to
communicate with the equipment, while the equipment could switch
high voltage devices in applications for displays, power control,
equipment control, systems engineering and so on.
[0006] The invention provides a CMOS circuit as set out in the
accompanying claims.
[0007] The invention relates generally to the combination of RF
devices and high voltage transistors in the same circuit. RF
devices include transistors; capacitors; inductors and variable
capacitors developed and characterised for these applications.
[0008] In the context of the accompanying claims, high voltage is
assumed to be greater than 8V, and low voltage is assumed to be
less than 8V. However, the invention also includes embodiments in
which the threshold between high and low voltage is assumed to be
5V, rather than 8V. That is, the invention also provides a CMOS
circuit as set out in the accompanying claims in which "5V" is
substituted for each occurrence of "8V".
[0009] Embodiments of the invention will now be more particularly
described, by way of example only, with reference to the
accompanying drawing, which shows low voltage, high voltage and RF
CMOS circuits formed on the same semiconductor substrate.
[0010] In one embodiment, a process developed for high voltage
applications is provided for fabricating such transistors which can
operate at voltages above the normal supply voltage. Typically this
means greater than 3.3V for 0.35 micron technology or greater than
1.8V for 0.18 micron technology. The process comprises a core CMOS
technology; combined with additional diffusions which either singly
or in multiple combinations provide the means to build transistors
which can operate with the drain at a high voltage; or in
combination with additional gate oxide thicknesses to enable the
input terminal of the transistor (gate in the case of a MOSFET or
base in the case of a bipolar) to operate at higher voltages also.
The use of multiple diffusions or "wells" enables both the source
and drain sides of a transistor to operate at high voltages. This
enables devices attached to the circuit to be controlled in the
high voltage line, when it is called a high side switch. Drain-only
devices can be used on the low side, called a low side switch.
[0011] In this patent such technologies are combined with
transistors characterised or developed and characterised for RF
applications. Transistors for this application means the layout of
a device; and characterisation of the device to develop models
suitable for circuit design called "compact models" to
differentiate between extensive, physics-based models collectively
called Technology Computer Aided Design (TCAD) and simpler models
used in circuit simulators like SPICE.
[0012] Transistors designed for RF include those where
consideration of the gate layouts and fingers has been taken into
account so as to minimise the gate impedance at RF; and metal
wiring to minimise parasitic capacitance which also impedes
performance. Characterisation of these devices at RF involves the
determination of additional components to account for time delays
arising due to a non-zero time-of-flight of electrons or holes
across the channel region of the transistor. Typically the
additional components needed are a gate resistance and substrate
resistance which provide an additional RC time delay to account for
non-quasi-static effects at high frequencies.
[0013] In the embodiment shown in the FIGURE low voltage 2, high
voltage 4 and RF 6 CMOS circuits are formed on a single substrate
8. A core CMOS process having a thick p-epitaxy 10 overlying the P+
substrate 8, and having two diffusion wells to form NMOS and PMOS
transistors is extended with two additional wells called a deep
lightly doped N well 12, and a deep lightly doped P well 14. Used
singly or in combination, it is possible to generate high voltage
transistors which can operate at medium voltages (14V) or high
voltages (50-80V). In addition, transistors intended for RF
applications are built in the core CMOS technology wells using
layout styles optimised for low gate resistance and low parasitic
capacitances. Together this forms a powerful combination of high
voltage devices which can support RF communication links.
[0014] A preferred embodiment is described. First, a substrate
comprising a silicon wafer which may be lightly doped or heavily
doped on which a lightly doped layer is grown, is oxidised. A
series of modules is added in which high voltage wells are
sequentially masked and implanted, photoresist cleaned off and
subsequently the implanted regions are diffused to a suitable depth
for the high voltage transistors.
[0015] Secondly, the normal CMOS process modules are processed in
which further layers of oxide and nitride are grown and deposited,
followed by patterning and a further thick oxide is grown. Normal
CMOS isolation regions are formed under the thick oxide regions and
regions where the thick oxide was prevented from growing. These
comprise regions of silicon which are doped more heavily but of
similar type to the said layer doping, or more heavily than the
said layer doping but of opposite type so that complementary
transistors can be made inside these regions.
[0016] Thirdly, one or more gate oxides are grown in order to
create insulating regions appropriate to the transistors required.
For example a 40 nm gate oxide may be required to sustain 20 V
while 7 nm may be needed for high performance 0.35 micron, 3.3V
transistors. These are formed by a first gate oxidation in which an
oxide of perhaps 39 nm is grown, followed by a masking and etch
stage which removes this oxide in regions where a thinner oxide is
required. Finally, the thin oxide layer is grown which is aimed at
the low voltage target. At the same time the thick oxide is
increased very slightly.
[0017] The next stage is to create low and high voltage transistor
gates. The RF transistors are built using standard masking layers
in optimised layouts. High voltage gates are also formed through
appropriate masking patterns. Some combinations of said low voltage
isolation diffusion regions can be utilised in high voltage
transistors by appropriate layout.
[0018] The process is continued with the formation of LDD regions,
spacers at the edges of the polysilicon gates; and silicidation of
the gates and active area diffusions. The process is largely
completed with the formation of inter-poly to metal dielectric
oxide layers, contact regions and metal interconnect lines with one
to three layers of metal. Optionally, a fourth layer can be used to
increase the interconnect routing capability. Optionally, further
layers can be used also. Optionally, the top layer of metal can be
made from a thicker metal layer than standard. This enables RF
specific components like an inductor to be provided which has an
acceptable Q-factor.
[0019] Optionally, a metal to metal capacitor can be included
between the metal layers whereby a thin dielectric material is
added to the metal at one or more stages. This creates a high
capacitance per unit area capacitor while offering very low
resistance electrodes, thus providing a high Q factor for RF
designs.
[0020] Using the RF devices with specific layout optimisation and
high voltage additional processes, this embodiment provides for RF
circuitry together with high voltage capability for a wide range of
remote linked applications in commercial and industrial
equipment.
* * * * *